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Forschungszentrum Jülich
Simultaneous Measurement of the Piezoelectric, Dielectric and Resistive Current Response ofDielectric and Resistive Current Response of
Ferroelectric Capacitors by an AFM Approach
A. Petraru1, H. Kohlstedt1,3 ,V. Nagarajan2, R. Ramesh3, D G Schlom4 K Szot1 and R Waser1D. G. Schlom4, K. Szot1 and R. Waser1
1 Institut für Festkörperforschung and CNI, Forschungszentrum Jülich GmbH,Jülich, Germany
2 School of Materials Science and Engineering University of New South WalesSydney NSW 2052
3 D t t f M t i l S i d E i i d D t t f Ph i3 Department of Materials Science and Engineering and Department of Physics,University of California, Berkeley, California 94720 USA
4 Department of Materials Science and Engineering Pennsylvania State University, U i it P k PA 16802 USAUniversity Park, PA 16802 USA
MRS San Francisco April_2006
Motivation
Non-volatile memory application of ferroelectric capacitorsand ferroresisitve storage devices
A: ScalingCharacterization of nano-scaled ferroelectric capacitorsCharacterization of nano scaled ferroelectric capacitorsd33, C, P vs. size
B: Ferroresistive storage devicesResistive switching:How to distinguish a ferroelectric origin from a non-ferroelectric one?
Sample Preparation
B. Liu et al., APL 80, 4801 (2002)
PbZr0.4Ti0.6O3 epitaxial (001) oriented films were prepared by sol-gel deposition.
Capacitors were made by focused ion beam (FIB) milling having lateral sizes between 10 μm – 200 nm
La0 5Sr0 5CoO3
Ptμm – 200 nm
La0.5Sr0.5CoO3
PbZr0.4Ti0.6O3
Top and base electrodes (PLD)
LaxSr1-xTiO3
Epitaxial conductive template layer (MBE),
La0.5Sr0.5CoO3
SiDarrell Schlom Penn State
Simultaneous Measurement of different Properties
A. Petraru et al., to be published in Appl. Phys. A
Laser U0 + umax sin (ωt)Detector
~ Lock-in 2
I / V Lock-in 1
PZTPt
SubstrateBase electrode
I-V converter
PZT
T d C d I ( i ti ) bi lt i lt lTo measure d33, C and I (resistive) vs. bias voltage simultaneously
An Example: d33 and C vs. V
8 area: 100 μm2
7
8
2x10-3
3x10-31000 C
2
d
6 1x10-3
2x10
800
900
12 F
)
d33
a.u.
)
r
4
5
-1x10-3
0600
700
(x 1
0-1
d 33 (aε r
3
4
3 10-3
-2x10-3
400
500 C
3 1
-4 -2 0 2 42 -4x10-3
-3x10 3
300 4
-4 -2 0 2 4U (V)
Jaehwan Oh and R. J. Nemanicha. J.Appl. Phys. 92, 3326, 2002.Rui Shao, Sergei V. Kalinin, and Dawn A. Bonnell. Appl. Phys. Lett., 82 1869, 2003.Ryan OHayre Minhwan Lee and Fritz B PrinzRyan OHayre, Minhwan Lee, and Fritz B. Prinz J.Appl. Phys. 95, 8382, 2004.
Area Dependence
1500
Peak dielectric constant
0 43
Coercive voltage
1300
1400
1500
ε r 0.41
0.42
0.43
age
[V]
1000
1100
1200
peak
ε
0.39
0.40
rciv
e vo
lta0.1 1 10 100
800
900
1000
2 0 01 0 1 1 10 100
0.37
0.38
Coe
rArea (μm2) 0.01 0.1 1 10 100
Area [μm2]
Ab f li f thNo significant scaling of the Absence of scaling of the coercive voltage.
No significant scaling of the dielectric constant.
B: Ferroresistive storage devicesResistive switching:How to distinguish a ferroelectric origin from a non-ferroelectric one?
4
Numerical modelExperimental result
2
3
[mA
]
-1
0
1
C
urre
nt
-2,0 -1,0 0,0 1,0 2,0
-2
-1
January, 2003
V lt [V] Voltage [V]
Although the curves look similar
R. Meyer
PZT (20/80)Pt
Thickness: 6.4 nm Although the curves look similar –its not a proof!SrRuO3
SrTiO3
Area: 3 µm2
Resistive Switching observed in Ferroelectrics:
Reproducible memory effect in the leakage
1. Complex OxidesReproducible memory effect in the leakage current of epitaxial ferroelectric/conductive perovskite heterostructuresYukio Watanabe, APL 66, 28 (1995).
Pt PZT N SrTiO3 Ferroelectric Memory Diode
Au/PLZT/LSCO
Pt-PZT-N-SrTiO3 Ferroelectric Memory DiodeK. Gotoh et al.,Jpn. J. Appl. Phys. 35, 39 (1996).
Transport properties of LaTiO3 films and heterostructuresA. Schmehl, APL 82, 3077 (2003).
2. Non-Oxide (Ferroelectric) Materials
Novel switching phenomena in ferroelectric Langmuir–Blodgett filmsLangmuir Blodgett filmsA. Bune et al., APL 67, 3975 (1995).
Nanoscale polarization manipulation and conductance switching in ultrathin films of aconductance switching in ultrathin films of a ferroelectric copolymerHongwei Qu,et al., APL 82 4322 (2003).
Non-volatile memory cells based on ZnxCd1-xS ferroelectric Schottky diodesP. van der Sluis, Appl. Phys, Lett., 82, 4089 (2003).E t APL 2004Erratum: APL 2004
Theoretical background not clear!
Resistive Switching (non-ferroelectric oxides)
Beck et al., APL 77, 139 (2000), IBM-Zürich, based on SRO/SrZrO3:Cr/SRO
S T i t l APL 85 317 (2004)S. Tsui, et al., APL 85, 317 (2004)Ag/LaCoO3/LaAlO3 (interface effect)
Simultaneous Measurement of different Properties
A. Petraru et al., to be published in Appl. Phys. A
Laser U0 + umax sin (ωt)Detector
~ Lock-in 2
I / V Lock-in 1
PZTPt
SubstrateBase electrode
I-V converter
PZT
T d C d I ( i ti ) bi lt i lt lTo measure d33, C and I (resistive) vs. bias voltage simultaneously
Resistive Switching and Ferroelectricityd vs Bias
8x10-4
1x10-3
d33 vs. Bias
4x10-4
6x10-4
u.)
2x10-4
0
2x10-4
d 33 (a
.u
-6x10-4
-4x10-4
-2x10
-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
-8x10-4
U (V)
SrRuO3
PZT (20/80)Pt
Thickness: 30 nmArea: 3 µm2SrRuO3
SrTiO3
Area: 3 µm2
Resistive Switching and Ferroelectricityd C vs Bias
8x10-4
1x10-3
4.5
d33, C vs. Bias
4x10-4
6x10-4
3.5
4.0
u.)
)
2x10-4
0
2x10-4
2 5
3.0
d 33 (a
.u
C (p
F)
-6x10-4
-4x10-4
-2x10
2.0
2.5
-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
-8x10-4 1.5
U (V)
SrRuO3
PZT (20/80)Pt
SrRuO3
SrTiO3
Resistive Switching and Ferroelectricityd C I vs Bias
8x10-4
1x10-3
1.0
1.24.5
d33, C, I res. vs. Bias
4x10-4
6x10-4
0.6
0.8
3.5
4.0
u.)
))
2x10-4
0
2x10-4
0.2
0.4
2 5
3.0
d 33 (a
.u
C (p
F)
I (μ
A)
-6x10-4
-4x10-4
-2x10
0 4
-0.2
0.0
2.0
2.5
-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
-8x10-4
-0.6
-0.4 1.5
U (V)
SrRuO3
PZT (20/80)Pt
Vc = -0.5V Vc = 0.6V
SrRuO3
SrTiO3
Increase Bias Voltage…
4
5
2
3
A)
1
0
1
I (m
A
-3
-2
-1
-1,5 -1,2 -0,9 -0,6 -0,3 0,0 0,3 0,6 0,9 1,2 1,5-4
U (V)
AFM
U (V)
Pt
PZT (20/80)
Pt
SrRuO3
SrTiO3
( )
Resistive Switching and Ferroelectricity
3x10-4
4x10-4
4
5
1x10-4
2x10-4
2
3a.
u.)
A)
-Vr
4
0
1x10
-1
0
1
d 33 (a
I (m
A
-2x10-4
-1x10-4
-3
-2
-1
-1,5 -1,2 -0,9 -0,6 -0,3 0,0 0,3 0,6 0,9 1,2 1,5-3x10-4 -4
U (V)Heat! U (V)
SrRuO3
Pt
PZT (20/80)
Pt ResistiveSwitching Vr
Heat!
Vc = -0.5V Vc = 0.6VSrRuO3
SrTiO3
Vr
Ferroelectric Switching
Resistive Switching and Ferroelectricity
Current density high enough
Pt
Current density high enough for heat generation?
SrRuO3
SrTiO3
PZT (20/80)
Estimation: I = 10 µA, rtip = 5 nmJ = I/A
J = 1.5 x 107 A/cm2
If current > 10 µA,heating affects cantilever deflectionheating affects cantilever deflection
Resistive Switching caused by Ferroelectricity?
Rhighnt
106
Rhigh RlowC
urre
Voltage
105
(Ωcm
)
104
ρ high
, low
(
10ρ
Pt
PZT
Pt 30 nm
10-6 1x10-5 1x10-4
103SrRuO3
SrTiO3
PZT
Area (cm2)
Resistive Switching: Filament Model
K. Szot, FZ JülichBreakdown points
Pt Ferroelectric PbZr0.20Ti0.80O3
p(if resistive switchingappears)
30nm
SrRuO3 PtSrRuO3
SrTiO3
Schematic cross-section Top view
D. M. Schaadt et al., J. of Vacuum Science & Technology B 22, 2030 (2004)
K. Szot et al. Switching the electrical resistance of individual dislocations in single-crystalline SrTiO3, to be published in Nature Materials
Resistive Switching: Filament Model
G. DearnaleyA. M. Stoneham andD. V. MorganRep. Prog. Phys.33, 1129 (1970).
G. Dearnaley,Thin Solid Films 3, 1161 (1969).
Summary
Simultaneous acquirement of the C(V) characteristics I(V)Simultaneous acquirement of the C(V) characteristics, I(V) and piezoresponse d33 (V) of ferroelectric devices using a
conductive AFM
Lateral size scaling of ferroelectric capacitors:
we find no significant scaling of the dielectric constant with the lateral size down to 200 nmsize down to 200 nm
we do not find a significant variation in the tunability of the dielectric constant;
absence of scaling of the coercive voltage (and hence coercive field)absence of scaling of the coercive voltage (and hence coercive field) with lateral dimensions.
Resistive switching in ferroelectric materials:Resistive switching in ferroelectric materials:
in case of resistive switching we are able to distinguish a ferroelectric from a
non-ferroelectric origin
AcknowledgementCenter ofNanoelectronic Systems forInformation Technologyg
Sponsors:Sponsors:
Volkswagen-Foundation:“Nano-sized ferroelectric hybrids” under contract number I/77 737.
J i t NSF DFG P j tJoint NSF-DFG Project:University of Berkeley (Material Science Department)
University of Aachen (RWTH)Research Center JülichResearch Center Jülich
„Displacive and Conductive Phenomena in Ferroelectric Thin Films:Scaling effects and switching properties“.